Typically, a conventional wire-cut electric discharge machine comprises a wire feed/drive system shown in FIG. 5, and is so arranged as to generate electric discharge between a wire 1 and a workpiece 106 for electric discharge machining while the wire 1 wound around a wire reel 101 rotatably supported by a column 100 is delivered by means of the wire feed/drive system. This wire feed/drive system comprises a brake device 102 consisting of a brake shoe and a brake pinch roller, a guide roller 103, upper and lower guide sections 104, 105, and upper and lower belt sections 108, 107 for wire feed. The lower belt section 107 is comprised of rollers r1-r3 and a belt stretched between these rollers, and the upper belt section 108 is comprised of rollers r4-r6 and a belt stretched therebetween, the roller r6 being coupled to a motor M2. Further, the wire feed/drive system comprises a wire guide 112, a feed roller 109 connected to a motor M1, and a pinch roller 110 disposed in urged contact with this roller.
During wire extension, the wire 1 is fed manually or by means of an automatic wire extension apparatus (not shown) from the upper guide section 104 toward an initial hole or the like, not shown, formed in the workpiece 106, and is then directed from the initial hole toward the upper and lower belt sections 108, 107 through a wire feed path in the lower guide section 105. Further, the wire is delivered under a condition that it is held between the belts of the belt sections which move with rotation of the motor M2, to be held between the feed roller 109 and the pinch roller 110 after passing the wire guide 112. After completion of wire extension in this manner, electric discharge machining is started, with the feed roller 109 and the upper belt section 108 driven by the motors M1, M2, respectively, so as to deliver the wire 1 held between the roller 109 and the pinch roller 110 and between the belts of the upper and lower belt sections 108, 107. The used wire then is cast away into a wire recover box 111.
As explained above, according to the conventional wire feed/drive system, the wire 1 is driven by the rollers 109, 110 and by the belt sections 108, 107 during electric discharge machining. Moreover, in order to feed the wire 1 in a stable manner, the motors M1, M2, associated with these rollers and the belt sections, respectively, are rotated in synchronism with each other. Further, the belt of each belt section is constructed so that two opposite ends thereof are connected in an endless manner, and hence a stepped portion is formed at the junction. Therefore, the belt is liable to rotate unevenly. Thus, even though the feed roller 109 is rotated accurately at a predetermined speed during the electric discharge machining, the wire feed speed is liable to vary, thereby possibly entailing variation in electric discharge machining characteristics. Moreover, since the wire and the belts are held in contact with one another, the belts can be easily worn away, and the wire can vibrate.